Allow fork in limited cases (#2624)

sanic/mixins/startup.py

@@ -40,9 +40,9 @@ from sanic.application.logo import get_logo
 from sanic.application.motd import MOTD
 from sanic.application.state import ApplicationServerInfo, Mode, ServerStage
 from sanic.base.meta import SanicMeta
-from sanic.compat import OS_IS_WINDOWS, is_atty
+from sanic.compat import OS_IS_WINDOWS, StartMethod, is_atty
 from sanic.exceptions import ServerKilled
-from sanic.helpers import Default
+from sanic.helpers import Default, _default
 from sanic.http.constants import HTTP
 from sanic.http.tls import get_ssl_context, process_to_context
 from sanic.http.tls.context import SanicSSLContext
@@ -88,6 +88,7 @@ class StartupMixin(metaclass=SanicMeta):
     state: ApplicationState
     websocket_enabled: bool
     multiplexer: WorkerMultiplexer
+    start_method: StartMethod = _default
 
     def setup_loop(self):
         if not self.asgi:
@@ -692,12 +693,17 @@ class StartupMixin(metaclass=SanicMeta):
         return any(app.state.auto_reload for app in cls._app_registry.values())
 
     @classmethod
-    def _get_context(cls) -> BaseContext:
-        method = (
-            "spawn"
-            if "linux" not in sys.platform or cls.should_auto_reload()
-            else "fork"
+    def _get_startup_method(cls) -> str:
+        return (
+            cls.start_method
+            if not isinstance(cls.start_method, Default)
+            else "spawn"
         )
+
+    @classmethod
+    def _get_context(cls) -> BaseContext:
+        method = cls._get_startup_method()
+        logger.debug("Creating multiprocessing context using '%s'", method)
         return get_context(method)
 
     @classmethod